Chromosome karyotype analysis of the genus <i>Rosa</i> L. sect. <i>Chinenses</i> germplasm resources

The chromosomal karyotype characteristics and phylogenetic relationships within 42 germplasm accessions from the genus Rosa L. sect. Chinenses were investigated through an integrative cytogenetic approach. Chromosome structural variation and evolutionary patterns were further assessed by combining karyotype clustering, a phylogenetic tree constructed based on SNPs, and fluorescence in situ hybridization (FISH) targeting ribosomal DNA (rDNA) loci. The analysis revealed that the chromosomes of sect. Chinenses are predominantly characterized by median and submedian centromeres, with low karyotype asymmetry indices, reflecting an overall conserved chromosomal architecture. Karyotype-based clustering offered partial resolution of ploidy levels and phylogenetic affinities among accessions, yet discrepancies were observed when compared with the SNP-derived phylogenetic tree, particularly in the delimitation between the ‘Ser. Chinenses’ and the ‘Ser. Odoratae.’ FISH results demonstrated that the number of 45S rDNA loci corresponded well with ploidy levels, while 5S rDNA loci were mainly localized in the centromeric regions. All accessions exhibited a collinear arrangement of 5S and 45S rDNA signals. In triploid accessions, the chromosomal locus composition mirrored that of R. chinensis var. spontanea, suggesting its potential role as a genomic donor. The combined application of karyotype analysis and rDNA-FISH proved effective in elucidating chromosomal evolutionary features within sect. Chinenses, providing valuable cytogenetic evidence for taxonomic classification and phylogenetic studies in Rosa.